Metallic composition for electrical contacts and the like



Patented June 30, 1942 r METALLIC COMPOSITION FOR ELECTRICAL CONTACTSAND THE LIKE Irvin W. Cox, West Allis, Wis., assignor to Cutler- Hammer,Inc., Milwaukee, Wis., a corporation of Delaware No Drawing. ApplicationJuly 3, 1941,

Serial No. 400,959

18 Claims. (Cl. 200-166) This invention relates to metallic compositionsfor electrical contacts and the like.

An object of the invention is to improve the life, current-controllingcapacity, and other operative characteristics of contacts formed ofcomposite materials molded in situ on base metal supports and adaptedfor use without sintering.

Another object is to provide an electrical contact formed of anunalloyed mixture of silver powder and a substance which acts, undermolding pressure, to wet the silver particles and provide an efficientbinder for the latter, while insuring proper and substantially uniformlow contact resistance and non-sticking characteristics of the contactwhen in use and throughout the useful life thereof.

Another object isto provide pressure molded contacts each consisting ofsilver and an associated substance which acts to minimize forma tion ofdebris as an incident to arcing therebetween when in use.

Another object is to provide a contact material adapted to be readilybrought to granular form by the application of heat to facilitatequantitative measuring and other handling thereof preparatory to moldingcontacts therefrom.

Another object is to provide electrical switch contacts which aresubstantially lower in cost than contacts formed of pure silver, whichwill have a much greater length of life than pure silver contacts, andwherein the tendency toward transfer or build-up between the contacts isminimized.

Another object is to provide electrical switch contacts containingconductive components and anti-flux components, which latter arecharacterized by their substantial insolubility, thermal stability attemperatures up to 1000 degrees F., and their ability when dissociatedunder the action of an arc to form volatile products,whereby relativelyclean arcing chambers are insured.

Other objects and advantages of the invention will hereinafter appear. 7

My invention consists essentially in the provision of a materialcomposed of silver and cadmium sulphide adapted for use in the form ofswitch contacts or the like. In practice the silver employed is inpowder form, and to the silver powder I add from a trace up to 20 perimprovement in up to 50 per cent of cadmium sulphide may be mixed withthe silver powder, in order to reduce the cost of the material whileretaining certain important advantages thereof. However, where thematerial is to be used in the form of switch contacts or contact tips Iprefer that the quantity of cadmium sulphide in the composition shallnot substantially exceed 20 per cent by weight of all the ingredients.Materials contain ing the aforementioned larger percentages of cadmiumsulphide will preferably be employed to form are interrupting elementsor tips to be associated with the contacts of circuit breakers,--asdistinguished from the current carrying contacts themselves. 1

In a preferred'form of my invention I employ the following ingredientsfor the mixture in the proportions given, by weight:

Per cent Merck's precipitated silver powder 67 Crystalline silver powderof 80 mesh and finer -Q 22 Cadmium sulphide 11 powder, in about thepercentage given, a molded contact of superior density is obtained..Such increased density of the material in the finished article hasobvious advantages in respect of mechanical resistance to wear, and inrespect of added resistance to pitting and/or transfer of p the contactmaterial normally resulting from arccent by weight of cadmium sulphide,when the material is intended to be used for the formation of switchcontacts.

According to another phase of my invention,

ing. At the same time, such pores as remain do not entrap gas, so thatcontacts composed of my improved material do not blister even if heatedto redness.

Using the aforementioned preferred percentages of ingredients, I firstgrind the relatively coarse crystalline silver powder along with thecadmium sulphide, in a ball mill or the like, whereupon the Merck'ssilver powder is added and thoroughly mixed with the other ingredientsuntil a homogeneous amorphous or powdery mass is obtained.

The aforementioned mass of mixture of powdered ingredients is difficultto handle by mechanical volumetric measuring means, due to the poor anduncertain flow characteristics thereof, and heretofore it has beenconsidered necessary to weigh out or otherwise manually measure theamount of material to be employed for each mold charge. However, due tothe peculiar nature of the cadmium sulphide and its action relatively tothe silver particles, I am enabled to effect formation of the mixedingredients into granules of substantially any desired size by merelyheating and tumbling the mixture on a wire mesh screen. The granules ofthe mixture may then be caused to flow by gravity under any suitablecontrol means responsive either to volume or weight to effect propercharging of the mold cavities in any well known manner.

The mold charges are subjected to a relatively high moldingpressure,-say, 40,000 pounds per square inch, either at roomtemperature, or, preferably, at a temperature of 400 degrees F.which ismuch below the melting point of any of the ingredients. Asaforeindicated, the cadmium sul-- phide has the peculiar property ofwetting the particles of silver, and thus forms an excellent binder forthe latter, whereas under the molding pressure the particles of cadmiumsulphide are likewise welded to each other.

In practice my improved contact tips are molded directly onto supportingmembers or carriers formed of a base metal, such as copper.

Contact tips when produced in accordance with my invention arepeculiarly free from the formation of debris as a result of arcingtherebetween when in use. It is believed that this desirable result isdue to the fact that any cadmium sulphide particles if dislodged ordisintegrated by the are are completely vaporized, so that no solidmatter capableof forming the usual arc debris is thrown off. g i aContact tips or the character herein disclosed are distinguished bytheir extremely high current controlling capacity, long life, andrelative freedom from transfer or pitting. For example, in numeroustests conducted by me I have found that pairs or sets of such contactsare readily capable of going through at least 350,000 complete cycles.without serious transfer or pitting due to arcing, making 300 amperesand breaking 100 amperes, direct current. This Very greatly exceeds theoperative capacity of any known contact materials, as is evidenced bythe fact that in a test of the character aforementioned the Governmentspecifications merely require that the contact tips shall go 20,000complete cycles of operation without serious transfer of the contactmaterial.

Although at present I prefer to employ cadmium sulphide in thecomposition, it is to be understood that in carrying out my invention,other materials having the combination of properties afforded by cadmiumsulphide, as above enumerated. may be substituted for the latter. Forexample, I may substitute for cadmium sulphide-zinc sulphide; silversulphide, lead sulphide and the like.

I claim:

1. An electrical contact composed of silver and cadmium sulphide, thequantity of cadmium sulphide being not in excess of 20 per cent.

2. An electrical contact composed of precipitated silver powder andcadmium sulphide, the quantity of cadmium sulphide being not in ex cessof 20 per cent.

3. An electrical contact comprising silver powder of a fibrous textureas the principal ingreclient and including a quantity of cadmiumsulphide not in excess of 20 per cent by weight of said ingredients.

4. An electrical switch element composed 0! silver and a trace up to 50per cent of cadmium sulphide.

5. An electrical switch element composed of precipitated silver powderand a trace up to 50 per cent of cadmium sulphide.

6. An electrical contact composed of precipitated silver powder of afibrous texture as the principal ingredient and including a trace up to20 per cent of cadmium sulphide.

7. An electrical contact composed of silver and about 11 per cent byweight of cadmium sul phide, said contact being characterized by freedomfrom arc-formed debris as an incident to normal use thereof.

8. A pressure molded electrical contact composed of a homogeneousmixture of silver powder and about 11 per cent of cadmium sulphide.

9. An electrical contact pressure molded from a homogeneous mixture ofmaterials comprising about 67 per cent of Merck's precipitated silverpowder, about 22 per cent of a crystalline silver powder of mesh andfiner, and about 11 per cent of cadmium sulphide.

10. An electrical contact pressure molded from a granular materialconsisting of a homogeneous mixture of about 89 per cent of precipitatedsilver powder and about 11 per cent of cadmium sulphide.

11. An electrical contact material comprising a homogeneous mixture ofprecipitated silver powder and from a trace up to 20 per cent by weightof cadmium sulphide, said mixture being further characterized by itsreduction to granules of the desired size for molding as an incident toheating and tumbling thereof.

12. An electrical contact adapted for use without sintering, comprisinga homogeneous mixture of precipitated silver powder and about 11 percent by weight of cadmium sulphide, said mixture being characterized bythe ability of said cadmium sulphide to wet the silver particles and actas a binder for the latter when said mixture is subjected to a moldingpressure.

13. An electrical switch contact adapted to be pressure molded in situupon a suitable base metal support, said contact consisting of asubstantially homogeneous mixture of about 67 per cent of Merck'sprecipitated silver powder, about 22 per cent of a crystalline silverpowder of ap proximately 80 mesh and finer, and about 11 per cent ofcadmium sulphide, said contact being characterized by its adaptabilityfor normal use thereof with sintering and by its freedom from arc-formeddebris as an incident to such normal use.

14, A cold molded electrical switch element of relatively great densityadapted for use without sintering thereof, said element being formed.from granules each consisting of a substantially homogeneous mixture ofa quantity of silver powder of fibrous texture, a quantity ofcrystalline silver powder of 80 mesh and finer, and a quantity ofcadmium sulphide, the quantity of cadmium sulphide being not in excessof 50 per cent.

15. A cold molded electrical switch contact of relatively great densityadapted for use without sintering thereof, said contact being formedfrom granules each consisting of a substantially homogeneous mixture ofa quantityof silver powder of fibrous texture, a quantity of crystallinesilver powder of 80 mesh and finer, and a quantity of cadmium sulphide,the quantity of cadmium sulphide being not in excess of 20 per cent.

16. A cold molded electrical switch contact of relatively great densityadapted for use without sintering thereof, said contact being formedfrom granules each consisting of a substantially homogeneous mixture ofa quantity of silver powder of fibrous texture, a quantity ofcrystalline silver powder of 80 mesh and finer, and a quantity ofcadmium, sulphide, the first mentioned quantity of silver powder beingabout 67 per cent, the second mentioned quantity of silver powder beingabout 22 per cent, and the quantity of cadmium sulphide being about 11per cent.

17. A cold molded electrical switch contact comprising an unalloyedcomposition containing conductive components and anti-flux components,the anti-flux components being characterized by their ability to wet thesurfaces of the conductive components and act as a binder therefor,whereby the contact is adapted for use without sintering thereof; saidantifiux components being further characterized by their thermalstability at temperatures up to 1000 degrees F.; and said anti-fluxcomponents being still further characterized by their ability todissociate at the arcing surface into one'or more volatile products,thus maintaining said arcing surface of substantially constantcomposition and substantially constant contact resistance as the contactwears, whereby the amount of arc debris deposited in the arc chamber isreduced to a 18. An electrical switch element composed'of precipitatedsilver powder, said-silver powder being characterized by its fibroustexture, extreme whiteness, and unusual ability to cold weld underpressure to a tough solid of considerable tensile strength, and a traceup to 50 per cent of cadmium sulphide.

' IRVIN W. COX.

